In the development of internal combustion engines, it is basically sought to minimize fuel consumption and reduce pollutant emissions. In the previous systems, various measures are implemented and concepts are used to achieve said aims.
With regard to the pollutant problem, the reduction of nitrogen oxide emissions is of high relevance, in particular in the case of diesel engines. Since nitrogen oxides form due to not only an excess of air but rather also high temperatures, one concept for reducing the nitrogen oxide emissions includes reducing the combustion temperatures.
Here, exhaust-gas recirculation (EGR), that is to say the recirculation of exhaust gases from the exhaust-gas discharge system into the intake system, is expedient in achieving this aim, wherein it is possible for the nitrogen oxide emissions to be considerably reduced with increasing exhaust-gas recirculation rate. Here, the exhaust-gas recirculation rate XEGR is determined as follows:XEGR=mEGR/(mEGR+mFresh air)
where mEGR denotes the mass of recirculated exhaust gas and mFresh air denotes the fresh air which is supplied, having previously been compressed by means of a compressor, to the at least one cylinder. Within the context of the present disclosure, therefore, the charge air may also comprise recirculated exhaust gas aside from the fresh air.
To obtain a considerable reduction in nitrogen oxide emissions, high exhaust-gas recirculation rates are utilized which may be of the order of magnitude of xEGR≈60% to 70%. According to the prior systems, to adjust the exhaust-gas quantity to be recirculated, that is to say the recirculation rate, a control element, also referred to as an EGR valve, is provided in the recirculation line. Exhaust-gas recirculation may also be utilized for reducing the emissions of unburned hydrocarbons.
Internal combustion engines may be equipped not only with at least one exhaust-gas recirculation arrangement but rather also with at least one exhaust-gas turbocharger which comprises a compressor arranged in the intake system and a turbine arranged in the exhaust-gas discharge system.
Supercharging is primarily a method for increasing performance, wherein the air for the combustion process in the engine is compressed, as a result of which the fuel mass supplied and the mean effective pressure can be increased. By means of supercharging, it is possible not only for the power of the internal combustion engine to be increased while maintaining an unchanged swept volume, but rather also for the swept volume of the internal combustion engine to be reduced while maintaining the same power. Supercharging basically leads to an increased specific power and to a more favorable power-to-weight ratio. For the same vehicle boundary conditions, it is thus possible by means of supercharging for the load collective to be shifted toward higher loads, at which the specific fuel consumption is lower.
Supercharging consequently assists in the constant efforts in the development of internal combustion engines to minimize fuel consumption, that is to say to improve the efficiency of the internal combustion engine.
In an exhaust-gas turbocharger, a compressor and a turbine are arranged on the same shaft. The hot exhaust-gas flow is supplied to the turbine via an exhaust line and expands in said turbine with a release of energy, as a result of which the shaft is set in rotation. The energy supplied by the exhaust-gas flow to the turbine and ultimately to the shaft is used for driving the compressor which is likewise arranged on the shaft. The compressor delivers and compresses the charge air supplied to it via the intake line, as a result of which supercharging of the at least one cylinder is obtained. A charge-air cooler is often provided downstream of the compressor, by means of which charge-air cooler the compressed charge air is cooled before it enters the combustion chamber, and therefore the density of the cylinder charge is increased.
The advantage of an exhaust-gas turbocharger for example in relation to a mechanical charger is that no mechanical connection for transmitting power exists or is used between the charger and internal combustion engine. While a mechanical charger draws the energy for driving it from the internal combustion engine, the exhaust-gas turbocharger utilizes the energy of the hot exhaust gases produced by the internal combustion engine.
Supercharging may also be used to reduce pollutant emissions. With targeted configuration of the supercharging for example of a diesel engine, the nitrogen oxide emissions can be reduced without any losses in efficiency. The hydrocarbon emissions can be favorably influenced at the same time. The emissions of carbon dioxide, which correlate directly with fuel consumption, likewise decrease with falling fuel consumption.
Accordingly, embodiments are disclosed herein that relate to harvesting excess energy from the engine that may otherwise be wasted, thus improving engine efficiency. In one example embodiment, an internal combustion engine having at least one cylinder, at least one exhaust line for discharging combustion gases via an exhaust-gas discharge system, and at least one intake line for supplying charge air via an intake system comprises at least one exhaust-gas recirculation arrangement which comprises a recirculation line which branches off from the exhaust-gas discharge system and which opens into the intake system; at least one exhaust-gas turbocharger comprising a compressor arranged in the intake system and a turbine arranged in the exhaust-gas discharge system; a throttle element which is arranged in the at least one intake line downstream of the compressor; a bypass line which branches off from the at least one intake line upstream of the throttle element and which opens into the at least one intake line again downstream of the throttle element; and an expansion machine for gaining additional energy arranged in the bypass line.
In the internal combustion engine according to the disclosure, an expansion machine is provided in the intake system, that is to say on the inlet side of the internal combustion engine. The expansion machine utilizes the energy bound in the compressed charge air in order to increase the power output of the internal combustion engine in the overall balance if the operation of the internal combustion engine permits this, is suitable for this or if there is a demand for additional energy. The over-run mode of the internal combustion engine is an example of an operating state which is suitable for the use of the expansion machine to gain additional energy which would otherwise remain unutilized.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.